These are Eclipse Update site URLs to be used inside the Eclipse IDE, these are not browser specific URLs. Eclipse pings the URL for a content.jar file which contains a manifest of the update site content. Then the plugins from OTN will be installed. As long as Eclipse can find this information, the update site is working.

Since these URLs are not supposed to be accessed through a web browser, then the 404 error is thrown, but probably some kind of landing page will be implemented for users who try to connect to the update site in their browsers.